Ultrastructural and molecular characteristics of crayfish photoreceptor membranes.

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Abstract
The ultrastructure of photoreceptor cells of the crayfish (Procambarus clarkii) was examined by thin sections and freeze-fracture. In the photoreceptor membranes there were particles associated primarily with the A faces of freeze-fracture preparations, which had a mean diameter of 80-84 .ANG. and a density of 6600/.mu.m2. Treatment of the retina with digitonin (a substance capable of extracting visual photopigments) in Ringer caused marked disruption of the hexagonal arrangement of the microvilli, breakdown of the microvilli into smaller segments and gradual removal of the particles. The estimated photopigment concentration in the microvillus was 4000/.mu.m2. The particles probably represent the photopigment in situ.